Mobile column measurements provide a means to characterize the distribution of trace gases over a large spatial scale while capturing the atmospheric variability over the column. Combined with wind measurements, mobile column measurements of trace gases have been shown to be very useful to constrain emission of trace gases from source regions by applying a mass conservation approach. Mobile column measurements from various platforms have previously been used to estimate: nitrogen oxides (NOx) emissions from cities; nitrogen dioxide (NO2), sulfur dioxide (SO2), and formaldehyde (HCHO) emissions from industries using the differential optical absorption spectroscopy (DOAS) technique; and fugitive volatile organic compound (VOC) emissions from refineries using the solar occultation flux (SOF) method. The DOAS method typically is limited to the UV-Vis wavelength region and uses scattered sunlight; while the SOF method uses direct sun observations in the mid-IR wavelengths.
DOAS measurements of scattered sunlight are particularly attractive for mobile column measurements, because scattered sunlight measurements do not require clear-sky conditions and because of the relative ease of operating such instruments. In particular, the stability of the elevation angle (EA), i.e., angle relative to the horizon, is less crucial at higher EAs typically used for mobile DOAS measurements. However, logistical challenges arise when measurements observe the direct solar beam from a moving platform, e.g., due to highly uncorrelated motions of vehicles on roads.
There is thus a need in the art for devices and techniques for detecting and measuring gas emissions in a vertical column using light source beams, from an unstable, moving platform. The present invention addresses this need.